Forum Discussion
Honored ContributorUART loses bytes
Hi
I have a problem with the uart: I can send single bytes from PC to FPGA and loop them back with out problem at baud rates up to 3MBd. But as soon as I write more than one byte at once or more bytes one after the other without delay, the FPGA loses some bytes. It gets worse with higher baud rates, but happens already at 9600Bd. my setup: - Cyclon II - Nios II - I use HAL to access the UART some suggestions would be great Thanks12 Replies
Altera_ForumAre you using blocking or non-blocking I/O?
- Altera_Forum
I'm using non blocking I/O on the FPGA. Blocking on the read because I'm polling for new data. Could this be the problem?
- Altera_Forum
Non-blocking implies that the send data are buffered and handled by an interrupt routine. You should check if everything is set up correctly.
- Altera_Forum
Thanks, I'll check this out. But does this have an influence on the receive?
- Altera_Forum
Hi
Unfortunately if I switch to blocking the same thing happens. I tried the communication in one direction from PC to NIOS. At 3MBd I always receive the last of 8Bytes on NIOS side. With smaller Bd rates more Bytes are received. - Altera_Forum
You should determine, if the data is possibly send out correctly and gets lost at the PC side. An oscilloscope or SignalTap are suitable tools.
- Altera_Forum
How can you connect the PC to the Cyclone?
I have Cyclone III starter board, the only available pins are the JTAG, the boundary scan pins. - Altera_Forum
JTAG UART is an option.
- Altera_Forum
Thanks fro your response. I understand that many uses that during design, but if I want to move my design to be final and get to an actual hardware, would I be still able to wire those JTAG and use them? In my design in real device there is not much data to be transferred to the FPGA, just few and no need for speed to do that.
- Altera_Forum
For a final design you can use a real RS232 line. You can still use the JTAG UART during development and switch once you have your hardware, the software isn't difficult to change.
